*Need an answer by the end of the day*

Anita purchased three bonds to form a portfolio as follows:

Bond A has a Macaulay duration of 20.50 years, and was purchased for $1985.

Bond B has a Macaulay duration of 10.35 years, and was purchased for $1015.

Bond C has a Macaulay duration of 11.75 years, and was purchased for $2000.

Calculate the Macaulay duration of the portfolio at the time of purchase.